The present invention is an improvement on the Gifford-McMahon cycle. Familiarity with said cycle is assumed. Representative prior art patents teaching such cycle include U.S. Pat. Nos. 2,966,035; 3,188,818; 3,218,815; and 4,305,741.
For maximum efficiency and reliability, it is important to have maximum gas volume transfer through the regenerator. In order that this may be attained, it is important that the direction of gas flow be reversed when the displacer is at top dead center or bottom dead center. The present invention is directed to a solution of that problem by utilizing an electric motor to control the position of the displacer adjacent top dead center and bottom dead center in combination with pressure from an independent source and a slidable pressure responsive valve for controlling fluid flow.